Power tool and motor controller

ABSTRACT

A method and apparatus to automatically reverse the motor of a power tool, such as a dispensing gun or similar tool. In some constructions, a controller automatically reverses the direction of plunger movement and removes the plunger from contact with the back wall of a cartridge. The controller has a trigger switch that is coupled to a power source, such as a battery, and includes a main power on/off switch and a potentiometer. A protection or secondary switch is coupled in parallel to the main power on/off switch. A power supply circuit and a commutator are each coupled to the main and secondary switches. An overload sensor is coupled to the commutator. The controller includes a programmable device that is coupled to the power supply circuit, the potentiometer, the commutator, and the overload sensor. The programmable device is operable to sense actuation and deactuation of the main power on/off switch, read an electromotive force from the potentiometer, and, upon sensing deactuation of the main switch, send a control signal to the commutator to reverse current flow therethrough for a predetermined amount of time, and deactuate the secondary switch when the predetermined time has lapsed.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/996,564, filed Nov. 23, 2004, which is a continuation-in-part of U.S.patent application Ser. No. 10/152,059, filed May 21, 2002, now U.S.Pat. No. 6,823,134, issued Nov. 23, 2004, which is a continuation ofU.S. patent application Ser. No. 09/731,438, filed Dec. 6, 2000, nowU.S. Pat. No. 6,392,373, issued May 21, 2002. The contents of theseapplications and patents are hereby incorporated by reference in theirentirety.

SUMMARY OF THE INVENTION

The present invention generally relates to methods and devices used tocontrol electric motors. More particularly, the invention relates tomethods and apparatus to automatically reverse an electric motor tocontrol the operation of a tool, such as, for example, a dispensing gun,a tube cutter, a saw, etc., driven by the motor.

Hand powered dispensing guns have been available for many years. Morerecently, pneumatic and electric versions of hand-powered dispensingguns have been made available. Most dispensing guns, whetherhand-powered, pneumatic, or electric, operate in a similar manner. Acartridge of material is placed in a cradle of the gun. The cartridgehas a nozzle on one end and a disk or back wall on the other. The gunincludes a plunger that is positioned coaxially with the back wall whenthe cartridge is placed in the cradle. The plunger contacts the backwall and moves it forward forcing the material in the cartridge out ofthe nozzle.

Electric-corded and battery-powered dispensing guns include an electricmotor controlled by a trigger-actuated switch. Pulling the triggercloses the switch and electrically interconnects the motor to the powersource. The motor drives a rack and pinion mechanism to advance theplunger. The plunger is thereby driven into the back wall of thecartridge to dispense the material. The operator can control theadvancement of the plunger into the material cartridge and, thereby,control the application of material to the desired surface. Powereddispensing guns typically incorporate a speed control mechanism thatallows the operator to control the speed of the flow of material out ofthe cartridge nozzle. As the operator becomes proficient with the tool,he or she can increase the speed at which the material is dispensed. Theoperator typically also has the option of retracting the plunger fromthe back wall of the cartridge. Operators remove the plunger from thecartridge when the cartridge is empty or when the job has beencompleted. Some dispensing guns have a manual switch to change thedirection of the motor, thereby changing the direction of the plungerand retracting it away from the cartridge. Other dispensing guns have amanual mechanical release that allows the operator to physically pullthe plunger out of contact with the cartridge.

While present dispensing guns are functional, they suffer from at leastone deficiency. In general, once material is dispensed from a dispensinggun the material continues to flow out of the gun's nozzle after thegun's trigger mechanism has been released. After-flow (or oozing at thedispensing tip) leads to waste of material, nozzle fouling, droppedmaterial, and additional clean up time.

Two primary reasons for the after-flow phenomenon are recognized. First,the usually thin-walled cartridge expands during plunger actuation and,according to the physical law that systems always attempt to return tothe relaxed state, the cartridge wall relaxes after the plungeractuation. Since the back walls of most cartridges are designed toretain their forward-most position and the plunger of the dispensing gunis typically locked against a return movement, the relaxation of thecartridge wall leads to after-flow. Second, most dispensed compositionshave a high viscosity and are at least marginally compressible. Thus,plunger actuation usually causes a substantial internal pressure buildupin the cartridge that, after the plunger is no longer forced forward,results in material leaking from the nozzle tip.

Accordingly, it would be desirable to have an improved method and deviceto control after-flow in a dispensing gun. In some aspects and in someconstructions, the invention provides a method and apparatus toautomatically reverse the motor of a dispensing gun for a predeterminedamount of time. An electronic motor controller automatically reversesthe direction of plunger movement and removes the plunger from contactwith the back wall of the cartridge. The automatic reversal of the motorto reverse plunger motion alleviates after-flow problems. The electronicmotor controller includes a trigger switch, a power supply circuit, acommutator, an overload sensor, and a programmable device.

The trigger switch is coupled to a power source, such as a battery, andincludes a main power on/off switch and a potentiometer. A protection orsecondary switch is coupled in parallel to the main switch. The powersupply circuit and the commutator are each coupled to the main andsecondary switches. The overload sensor is coupled to the commutator andthe programmable device. The programmable device is coupled to the powersupply circuit, the potentiometer, the commutator, and the overloadsensor. The programmable device is operable to sense actuation anddeactuation of the main power on/off switch, read an electromotive forcefrom the potentiometer, and, upon sensing deactuation of the mainswitch, send a control signal to the commutator to reverse current flowtherethrough for a predetermined amount of time. The programmable devicealso deactuates the secondary switch when the predetermined time haslapsed. Reversing the direction of the motor upon release of the triggerswitch reverses the direction of the plunger and stops forward movementof the back wall of the cartridge in the dispensing gun. As noted,automatically stopping the forward movement of the back wall alleviatesafter flow problems.

In some aspects and in some constructions, the invention may also beimplemented in a method including sensing actuation of the triggerswitch, reading a voltage from the trigger switch, generating a firstcontrol signal if the voltage from the trigger switch is equal to orgreater than a predetermined value, sending the first control signal toa commutator to drive an electric motor in a first direction, generatinga second control signal if the voltage from the trigger switch is equalto or less than a predetermined cut-off value, sending the secondcontrol signal to the commutator to drive the electric motor in a seconddirection, opposite the first direction, for a predetermined amount oftime, and deactuating the secondary switch when the predetermined timehas lapsed.

As is apparent from the above, it is an independent advantage of thepresent invention to provide an electronic motor control toautomatically reverse a motor to prevent after-flow of material from atool such as a dispensing gun.

Other independent features and independent advantages of the presentinvention will become apparent by consideration of the detaileddescription and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a power tool, such as a battery-powereddispensing gun.

FIG. 2 is a schematic drawing of an apparatus embodying one or moreindependent aspects of the invention.

FIG. 3 is a detailed circuit diagram of an apparatus embodying one ormore independent aspects of the invention.

FIG. 4 is a flow chart of software used in one or more independentaspects of the invention.

FIG. 5 is a graph of potentiometer (wiper) voltage versus travel.

FIG. 6 is a graph of duty cycle versus trigger travel.

FIG. 7 is a side partial cross-sectional view of an alternateconstruction of power tool, such as a tube cutter.

FIG. 8 is a flow chart illustrating the operation of a power tool, suchas the tube cutter shown in FIG. 7.

FIG. 9 is a side partial cross-sectional view of another alternateconstruction of power tool, such as a tube cutter, illustrated in afirst condition.

FIG. 10 is a side partial cross-sectional view the power tool shown inFIG. 9 illustrated in a second condition.

FIG. 11 is a flow chart illustrating the operation of a power tool, suchas the tube cutter shown in FIGS. 9-10.

FIG. 12 is a side partial cross-sectional view of yet another alternateconstruction of power tool, such as a tube cutter.

FIG. 13 is a flow chart illustrating the operation of a power tool, suchas the tube cutter shown in FIG. 12.

FIG. 14 is a flow chart illustrating the operation of a furtheralternative construction of a power tool, such as a saw.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the drawings. Theinvention is capable of other embodiments and of being practiced or ofbeing carried out in various ways. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limited. The use of“including,” “comprising” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. The terms “mounted,” “connected” and“coupled” are used broadly and encompass both direct and indirectmounting, connecting and coupling. Further, “connected” and “coupled”are not restricted to physical or mechanical connections or couplings,and can include electrical connections or couplings, whether direct orindirect.

In addition, it should be understood that at least some embodiments ofthe invention include both hardware and electronic components or modulesthat, for purposes of discussion, may be illustrated and described as ifthe majority of the components were implemented solely in hardware.However, one of ordinary skill in the art, and based on a reading ofthis detailed description, would recognize that, in at least oneembodiment, the electronic based aspects of the invention may beimplemented in software. As such, it should be noted that a plurality ofhardware and software based devices, as well as a plurality of differentstructural components may be utilized to implement the invention.Furthermore, and as described in subsequent paragraphs, the specificmechanical configurations illustrated in the drawings are intended toexemplify embodiments of the invention and that other alternativemechanical configurations are possible.

A power tool, such as, for example, a dispensing gun 10, incorporating amotor controller embodying one or more independent aspects of theinvention is illustrated generally in FIG. 1. As shown, the dispensinggun 10 includes a pistol-shaped housing 12, including a handle 14 and adrive enclosure 16, and a sleeve or cradle 18 that extends from thedrive enclosure 16. The cradle 18 is sized to receive commerciallyavailable tubes or cartridges of caulk, adhesive, and other similarmaterials. The cradle 18 includes an aperture 20 through which thenozzle N of a cartridge C projects. Components of the dispensing gunmounted within the drive enclosure 16 include a DC brush motor (notshown), a motor controller (discussed below), a drive linkage (notshown), and a drive rod 30. The dispensing gun 10 utilizes a rack andpinion mechanism (which includes the drive rod 30 and the drive linkage)driven by the DC brush motor to drive a plunger 32 coupled to theforward end of the drive rod 30 into the back wall 34 of the cartridgeC. A battery B is coupled to the handle 14. A finger-actuated triggerswitch 36 is mounted on the forward side of handle 14.

A motor controller 40 embodying independent aspects of the invention isshown in FIG. 2. The motor controller 40 can be powered by a variety ofsources, such as, for example, a cordless power tool battery (e.g., 12volt, 14.4 volt, 18 volt, etc.). The motor controller 40 generallyincludes the trigger switch 36, a zero battery drain/auxiliary powercircuit 44, a power supply circuit 46, a commutator 48, an overloadsensor 50, and a programmable device 55. The motor controller 40controls a motor M, which in the illustrated embodiment is a DC brushmotor. The functional blocks of FIG. 2 correspond to the blocks shown inbroken lines in the detailed circuit schematic of FIG. 3.

The trigger switch 36 is coupled to the battery B and includes a mainpower on/off switch 60 and a potentiometer 62 having a wiper 64. Theoperator inputs control information to the motor controller 40 throughthe trigger switch 36. The main power on/off switch 60 is closed whenthe operator depresses the trigger switch 36 and the main power on/offswitch 60 remains closed until the operator releases the trigger switch36 to a predetermined point. The main power on/off switch 60electrically couples the motor controller to the battery B when it isclosed. The distance the operator depresses the trigger switch 36correlates to the movement of the wiper 64 on the potentiometer 62.

As best seen by reference to FIG. 3, the electromotive force or voltageoutput by the potentiometer is based on the wiper voltage, at node POT4, with respect to the voltages at nodes POT 3 and POT 5. Node POT 5 isthe wiper ground reference and node POT 3 is equivalent to the upperrail voltage VCC supplied to the programmable device 55, which in oneembodiment is 5 volts. The programmable device sets the wiper groundreference, node POT 5, to 0 volts to utilize the full 0-5 volt range fordetermination of operator actuation of the trigger switch 36. The fullrange of voltage is desirable for greatest resolution in determinationof the trigger position. The farther the operator depresses the triggerswitch, the greater the reading of the wiper voltage at node POT 4 willbe. FIG. 5 illustrates a graph 70 having a horizontal axis 72 (travel),vertical axis 74 (voltage), and a curve 76. As can be seen by referenceto curve 76, the trigger switch 36 exhibits a substantially linearresponse of wiper voltage versus travel. The curve 76 illustrates thatthe operator must depress the switch a certain distance before a wipervoltage is produced (a threshold voltage). One embodiment requires thatthe wiper voltage reading at node POT 4 be at least one volt before thecommutator 48 receives a control signal to drive the motor in theforward direction. This minimum turn-on voltage requirement is utilizedto prevent tool operation due to an unintended trigger actuation. Themotor controller 40 is also designed such that a wiper voltage readingof below 0.2 volts is necessary to deactivate the motor M (thecommutator no longer receives a control signal from the programmabledevice 55 to drive the motor in the forward direction).

The transition from and variability between a high turn-on voltage and alow cut-off voltage (or hysteresis) is utilized in the invention toprevent the nuisance of on-off cycling of the tool when the operator isattempting to finely feather the material onto a work surface. Ifhysteresis was not utilized, the motor controller might instruct thecommutator to reverse the direction of the motor (as discussed ingreater detail below) when the operator only intended to slightly reducethe speed of the flow of material. The lower turn-off voltage allows theoperator to operate the tool just above the minimum turn-on voltage andthen reduce the speed to a certain degree when necessary to achievedesired material delivery results. The operator can vary the distancethe trigger switch 36 is depressed during operation of the tool to varythe speed at which material is dispensed. As illustrated by FIG. 5, whenthe trigger switch is fully depressed the maximum wiper voltage isobtained (see point 78). The maximum wiper voltage correlates to themaximum speed at which the motor M will operate. Once the 1 volt minimumturn-on voltage requirement is met, 0.2 volts correlates to the minimumspeed at which the motor will operate.

The zero battery drain/auxiliary power circuit 44 is coupled in parallelto the main power on/off switch 60 and includes a secondary switch 80and a relay 82. The secondary switch 80 is utilized to electricallycouple the motor controller 40 to the battery B during reversal of themotor. The motor controller 40 is designed to automatically reverse themotor when the operator has released the trigger switch and otherconditions (discussed below) have been met. When the trigger switch 36is released the main power on/off switch 60 will be opened and does notelectrically couple the motor controller 40 to the battery B. However,since the secondary switch 80 is mounted in parallel to the main poweron/off switch 60, the secondary switch 80 is capable of electricallycoupling the motor controller 40 to the battery B. To avoid the nuisanceof the motor M automatically reversing when not necessary, such as afteran unintended trigger actuation, the secondary switch 80 is closed onlyif the operator depresses the trigger switch a minimum distance for acertain amount of time. Although these settings could be varieddepending upon the application at hand, in one embodiment, theprogrammable device 55 does not send a control signal to the relay 82 toclose the secondary switch 80 until a one volt wiper voltage is read fora minimum of two seconds. The secondary switch 80 then remains closeduntil the programmable device 55 sends a control signal to the relay 82to open the secondary switch 80. This control signal is sent after themotor M has been reversed for the predetermined amount of time. When thesecondary switch is opened the motor controller 40 is not electricallycoupled to the battery B and the battery drain is reduced to zero.

The power supply circuit 46 is coupled to the main power on/off switch60, the secondary switch 80, the overload sensor 50, the commutator 48,and the programmable device 55. The power supply circuit 46 is includedin an integrated circuit 86 (see FIG. 3) that serves not only as avoltage regulator for the programmable device, but also as a levelshifter for the pulse-width modulation signal for the commutator, and acurrent limiting control. The voltage regulator portion of theintegrated circuit 86 converts the cordless tool battery voltage intothe appropriate upper rail voltage VCC for the programmable device. Theintegrated circuit 86 for one preferred embodiment is a TexasInstruments TL3843 Current-Mode PWM Controller.

A commutator suitable for use in the illustrated construction is an Hbridge, a specific example of which is a solid state dual MOSFET bridge.The commutator 48 is coupled to the motor M and controlled by theprogrammable device 55. When the motor M is being driven in the forwarddirection, a high side P-Channel MOSFET Q3 remains fully on to reducepower dissipation, and a low side N-Channel MOSFET Q2 is driven by apulse-width modulation signal of varying duty cycle from the circuit 86.The duty cycle of the pulse-width modulation signal correlates to thedistance the trigger switch 36 is depressed by the operator and,therefore, correlates to the speed at which the operator desires todispense material. The higher the desired speed of the tool is, thecloser to 1 the duty cycle of the pulse-width modulation will be. FIG. 6illustrates a graph 88 with a horizontal axis 90 (travel), vertical axis92 (percentage of duty cycle), and a response curve 94. The responsecurve 94 of FIG. 6 (percentage of duty cycle versus the travel of thetrigger switch) is not linear (in contrast to the response of the wipervoltage versus the travel of the trigger switch illustrated in FIG. 5).The programmable device 55 utilizes a look-up table to correlate thewiper voltage reading to the appropriate duty cycle. The exponentialtype response of the response curve 94 is utilized for greaterresolution of motor speed at the low end of trigger travel. The highdegree of resolution assists the operator in delivery of the material tothe desired surface. Especially for an inexperienced operator who is notcompletely oriented to the tool, the exponential response allows theoperator to lay a more uniform bead of material. When the motor M isdriven in the reverse direction the high side P-Channel MOSFET Q3 andthe low side N-Channel MOSFET Q2 are turned fully on to provide a fullpower reverse direction of the motor M for the predetermined amount oftime. The motor M is driven in reverse until the commutator 48 and themotor controller 40 are removed from electrical interconnection with thebattery B, which occurs when the secondary switch 80 is opened.

The overload sensor 50 is coupled to the commutator 48 and the circuit86. A current sense resistor samples the motor current directly. Thesampled current is then filtered and conditioned. The maximum currentdraw by the DC brush motor in one embodiment is 3.0 amps. When the motorcurrent is below this threshold, the threshold detector and currentsense circuitry of the overload sensor 50 deliver a logic state 0 signalto I/O pins of the circuit 86 and the programmable device 55. If the I/Opin logic state is 0, the motor M is driven at the current pulse-widthmodulation duty cycle. If the motor current is above the maximum currentdraw threshold, the threshold detector and current sense circuitrydeliver a logic state 1 signal to the I/O pins of the circuit 86 and theprogrammable device 55. The current limiting control circuitry of thecircuit 86 adjusts the pulse-width modulation duty cycle to limit thecurrent delivered to the motor M to the predefined maximum current draw.The programmable device 55 begins to decrement a timer such as a twosecond timer. If the timer is depleted, the programmable device 55 takesover the current limiting control function by folding back the currentof the motor to 10% of the maximum current draw value. Once currentlimiting control is taken over by the programmable device 55, the onlyway the operator can regain control of the tool speed is by fullyreleasing the trigger switch 36, which resets the motor controller 40.

One purpose of the overload sensor 50 is to prevent a force greater than500 lb/in² from being applied by the plunger to the back wall 34 of thecartridge C. The battery-operated dispensing gun 10 illustrated in FIG.1 is capable of producing approximately 2600 lb/in² of force deliverableby the plunger. If an operator of the dispensing gun was able to utilizeall of this force the cartridge could burst with a resultant mess andloss of material. The likelihood of such a mishap increases when thematerial in the cartridge has a low viscosity, the material is frozen,or the nozzle N is plugged. The motor controller 40 is designed to cutback power of the drive mechanism if an overload condition persists.Regardless of how far the operator depresses the finger actuated triggerswitch 36, the motor M will only be driven at 10% of maximum power if anoverload condition is recognized for more than two seconds.

The programmable device 55 is coupled to the power supply circuit 46,the potentiometer 62, the commutator 48, the relay 82 of the zerobattery drain/auxiliary power circuit 44, and the overload sensor 50.The programmable device 55 is operable to sense the actuation anddeactuation of the main switch 60, read an electromotive force from thepotentiometer 62, and upon sensing deactuation of the main on/offswitch, send a control signal to the commutator 48 to reverse currentflow therethrough for a predetermined amount of time. After the currenthas been reversed through the commutator 48 for the predetermined time,a different control signal is sent to the relay 82, which opens thesecondary switch and disconnects the motor controller 40 from thebattery B. Power to the motor controller 40 is shut off so the battery Bis not drained when the tool is not in use. In the preferred embodiment,the programmable device 55 is a Zilog 16 MHz Z86C83 micro-controller.

The software used by the programmable device 55 to operate the motorcontroller 40 is illustrated in the flow chart of FIG. 4. Before thesoftware is executed, the motor controller 40 is powered up. In order topower up the motor controller 40, the operator must depress the triggerswitch 36 as shown in step 150. The main power on/off switch 60 isclosed when the trigger switch 36 is depressed, coupling the battery Bto the motor controller 40.

As shown at step 154, Power Up Register Initialization, the softwareperforms initialization by setting-up and configuring the systemregisters of the programmable device 55. The system registers includethe hardware port control registers, port I/O registers, various timerregisters, and the interrupt control registers. The programmable device55 system registers are used for operation of the programmable device 55and for interfacing of the programmable device 55 with the othercomponents of the motor controller 40.

As shown at step 158, Application Register Initialization, the softwareclears all general-purpose programmable device registers and sets up andconfigures programmable device registers used for the automatic motorreversal application. Registers are specifically initialized with valuesfor TRIGGER ON TIME, TRIGGER READ TIME, and CURRENT OVERLOAD TIME. Theregisters initialized with these values act as timers that can bedecremented once a certain condition is met. For example, TRIGGER ONTIME is initialized to 2000, which corresponds to two seconds. If theprogrammable device 55 senses the main power on/off switch 60 is on andthe potentiometer wiper voltage is greater than one volt, the TRIGGER ONTIME timer is decremented. If the above conditions continue and theTRIGGER ON TIME timer is depleted, the secondary switch is closed andthe programmable device 55 performs a motor reverse.

As shown at step 162, Trigger Enable and Read Initialization, thesoftware initializes the registers that are required to performanalog-to-digital conversion of the wiper voltage (node POT 4) read fromthe potentiometer 62. The software also enables the external triggerswitch potentiometer wiper ground reference pin, which is electricallycoupled to a pin of the programmable device 55. The pin is set to thelogic 0 state. Setting the potentiometer ground to the logic 0 stateallows for a full 0-5 volt range to be applied to the trigger switchpotentiometer wiper. Allowing for the full five-volt range increases theresolution of speed control the operator can achieve.

As shown at step 166, Trigger Read, Duty Cycle Look-up and OverloadCheck, the software executes functions that occur during normaloperation of the tool. Specifically, the software performs a read of thecurrent trigger switch position, determines a new pulse-width modulationduty cycle for driving the motor, and checks the overload sensor.

The Trigger Read aspect of step 166 performs an analog-to-digitalconversion of the voltage (node POT 4) read from the trigger switchpotentiometer wiper. The wiper voltage will range from 0-5 volts. Thecurrent trigger position corresponds to the wiper voltage read, 0 voltscorresponds to a trigger switch that is fully released or inadvertentlyslightly depressed (less than 0.1 inches), and 5 volts corresponds to afully depressed trigger switch. The result of the analog-to-digitalconversion is analyzed to determine if code execution should transferback to perform further analog-to-digital conversions of the wipervoltage, perform a Duty Cycle Look-up, or perform a motor reverse.

If the software determines that the wiper voltage (node POT 4) isgreater than the minimum turn-on level, a Duty Cycle Look-up executes.The software determines what the duty cycle should be for the currenttrigger switch position. The current wiper voltage obtained in theTrigger Read is compared to a stored, predefined table of wiper voltagesand corresponding duty cycle values. When the current wiper voltagematches a voltage in the look-up table, the value of the duty cycleassociated with that voltage is stored in a timer register. This timerregister is used to control an internal timer used in step 170, MotorForward, to control the duty cycle of the pulse-width modulation signalthat drives the low side N-channel MOSFET Q2.

If a Duty Cycle Look-up is performed then the condition has been met forthe TRIGGER ON TIME timer to be decremented. If the value of the wipervoltage obtained via a Trigger Read remains above the turn-on leveluntil the TRIGGER ON TIME timer is depleted, the programmable device 55sends a control signal to the relay 82 to close the secondary switch 80.After the secondary switch 80 has closed, if the trigger switch is fullyreleased, execution transfers to step 174, Motor Reverse. If the wipervoltage does not reach the minimum turn-on voltage for the defined time,execution is not transferred to step 174.

Once the above steps are completed, an overload condition check isconducted on the motor M. The current draw of the motor is to be keptunder the maximum current draw to limit the force the plunger exerts onthe back wall 34 of the cartridge C. The software performs thisoperation by checking the logic state of the I/O pin connected to theoverload sensor 50. If the software detects a logic state 0, no furtheraction is performed and code execution is transferred to step 170, MotorForward. If the software detects a logic state 1, the CURRENT OVERLOADTIME timer initialized in step 158 is decremented and execution istransferred to step 170. If the software detects a logic state 1 at theI/O pin connected to the overload sensor 50 long enough to deplete thetimer, a predefined, relatively low duty cycle is loaded into theinternal timer register. Once the predefined duty cycle is loaded intothe internal timer register no further duty cycle lookups are performed.Rather, the duty cycle is fixed at the predefined low level to preventmotor overload. The duty cycle stays in this state until the operatorfully releases the trigger switch 36, thereby resetting the motorcontroller 40. Execution is similarly transferred to step 170 to performthe Motor Forward control. However, as explained above, the speed of themotor will only be at 10% of full power.

At step 170, Motor Forward, the software configures and sendsappropriate signals to the I/O pins that control the commutator 48 andgenerates the duty cycle. After the software has configured the I/O pinsfor forward operation of the motor M, the software turns the high sideP-Channel MOSFET Q3 fully on to reduce power dissipation. The softwaresends a pulse-width modulation signal to the low side N-Channel MOSFETQ2 to provide a variable speed function. The duty cycle of thepulse-width modulation signal is determined by using the duty cycle fromthe look-up table loaded into the internal timer at step 166. After asingle period of the duty cycle is completed, the software decrementsthe TRIGGER READ register counter initialized in step 158 and returns tostep 170 and performs another period of the duty cycle. Once the TRIGGERREAD register counter is depleted, execution is transferred back to step166. A new trigger switch position is then determined and, if the valueof the wiper voltage is above the turn-on level, a new duty cycle isdetermined from the look-up table. The new duty cycle is loaded into theinternal timer register. Code execution is then again transferred backto step 170 with the new duty cycle loaded and the motor control I/O pintiming adjusted accordingly. This cycle repeats itself until one of theconditions noted causes the cycle to end.

At step 174, Motor Reverse, the I/O pins that control the commutator 48and disable the relay 82 are configured. After the software hasconfigured the pins for reverse operation of the motor M, the softwareturns on the high side P-Channel MOSFET Q3 and the low side N-ChannelMOSFET Q2 fully for a predefined time. The predefined time of thepreferred embodiment is 0.5 seconds. The predefined time needs to belong enough to drive the plunger in reverse until it is no longer incontact with the back wall of the cartridge C. It is advantageous toreverse the motor only long enough to move the plunger from contact withthe back wall 34 of the cartridge C. If the motor reverses further thanthe necessary distance, time is wasted driving the plunger forward tothe back wall of the cartridge when the operator wishes to resume use ofthe tool. The predefined time is stored in a timer register initializedin step 158. Once that timer register is depleted, the software sends acontrol signal to the relay 82, disabling the relay 82 and therebyopening the secondary switch 80. These actions disconnect the motorcontroller 40 from electrical interconnection with the battery B. Themotor controller is powered down when the tool is not being used toprevent unnecessary draining of the battery power.

In addition to the features noted above, the controller 40 maybeconfigured with additional features such as an auto-reverse disablemechanism, a nozzle blowout mechanism, and a software trigger lock. Asbest seen by reference to FIG. 3, the programmable device 55 has severalavailable input pins that may be used to input additional informationregarding desired operating features. For example, the programmabledevice 55 may receive a disable signal from a switch (not shown) orsimilar device along a disable line DISABLE. Upon reading a signal onthe pin associated with the disable signal, the programmable device,when properly programmed to react to the condition of having a disablesignal, deactivates, or ignores those conditions that cause the deviceto reverse the motor when the trigger switch is released. Anauto-reverse disable feature might be useful when a dispensing gun isused at low speeds to apply small amounts of material.

In addition to a disable switch, a nozzle blowout input could besupplied through a switch (not shown) or similar mechanism to overridethe current overload functions of the invention. When so configured, thecontroller 40 would allow an operator to apply maximum current to themotor and, therefore, maximum force to the plunger to forcefully drivethe back wall of the cartridge. Such a feature would be useful to cleara plugged nozzle of a cartridge. Finally, the controller could beconfigured with a software trigger lock. Such a lock could be configuredsuch that the tool would not operate until appropriate inputs from thetrigger switch or other inputs mechanisms were received by theprogrammable device 55. Such a trigger lock would enhance safety byreducing inadvertent actuation of the device controlled by thecontroller 40. A software trigger lock could also act as a theftdeterrence device, making it nearly impossible for individuals lackingknowledge of the software unlock inputs to use the device.

It should be apparent from the discussion above and to those of ordinaryskill in the art that the exact configuration of the controller could bevaried. For example, many of the individual components described abovecould be combined on a single integrated circuit or chip and featuresand components could be implemented in either hardware or software. Itshould also be recognized that the controller 40 could be utilized inother electric tools, not just dispensing guns, in which an automaticreverse function would be of benefit.

FIG. 7 illustrates a tube cutter 200 embodying one or more independentaspects of the invention. The tube cutter 200 includes a housing 204,which is generally pistol-shaped. The housing 204 includes a handle 208and a trigger 212.

The housing 204 includes a cradle or tube support portion 216, whichsupports a tubular structure 220 for a cutting process. The tube supportportion 216 is configured to receive any size tubular structure. It isnoted that the tubular structure 220 is not limited to having a circularcross-section but also includes structures with non-circularcross-sections.

The housing 204 supports a motor 224 (e.g., a DC motor) and a motorcontroller 228. The motor controller 228 is similar to or the same asthe motor controller 40 described above. The motor controller 228 caninclude the same or similar components as the motor controller 40 andcan be modified for application and use in the tube cutter 200. Themotor controller 228 operates in the same or similar manner as the motorcontroller 40. The motor 224 and the motor controller 228 can be poweredby a variety of sources such as a battery 232 (e.g., 12 volt, 14.4 volt,etc.). The battery 232 may be coupled to the handle 208.

In the illustrated construction, the housing 204 supports a tube cuttingmechanism operable to cut the tubular structure 220. The tube cuttingmechanism may be similar to that disclosed in U.S. Pat. No. 6,189,216,the entire contents of which is hereby incorporated by reference.

In the illustrated construction, a pair of rolls 236 is driven by themotor 224. The rolls 236 include respective axes 240, 244 that areoriented in a direction that is parallel to one another. The axes 240,244 are also oriented in a direction that is parallel to an axis of thetubular structure 220 that is to be cut by the tube cutter 200.

In the illustrated construction, the housing 204 includes a rotatableblade 248 that is supported on a rod 252 and that can be moved into andout of engagement with the tubular structure 220 that is to be cut.Movement of the rod 252 is controlled by the motor 224. The rod 252 ismoved from a start or home position (a first condition of the cuttingmechanism) toward the rolls 236 until the blade 248 engages the tubularstructure 220 and moves the tubular structure 220 into drivingengagement with the rolls 236. The rolls 236 rotate the tubularstructure 220, and the rod 252 and the blade 248 continue to advanceinto the wall of the tubular structure 220 until the cutting operationis complete (a second condition of the cutting mechanism). As describedbelow, when the cutting operation is complete, the controller 228automatically reverses direction of the motor 224 to move the rotatableblade 248 and the rod 252 away from and out of engagement with thetubular structure 220 (e.g., operating the cutting mechanism from thesecond condition to the first condition).

FIG. 8 is a flow chart illustrating the operation of the tube cutter 200to cut a tubular structure 220. The operator positions (at 260) atubular structure 220 in the tube support portion 216. The operatoractuates (at 264) the trigger 212, which couples (at 268) the battery232 to the motor controller 228 and the motor 224. With the trigger 212continuously actuated, the motor 224 moves (at 272) the rod 252 towardthe tubular structure 220 until the blade 248 engages the tubularstructure 220 and rotates (at 276) the pair of rolls 236. The rod 252and the blade 248 continue to advance, and the blade 248 cuts (at 280)the tubular structure 220 as the tubular structure 220 is rotated.

When the tubular structure 220 is severed (the second condition of thecutting mechanism), the operator releases (at 284) the trigger 212, andthe motor 224 automatically reverses (at 288) direction. The rod 252 andblade 248 automatically moves (at 292) out of engagement with thetubular structure 220 so the operator can remove the tubular structure220 from the support portion 216. As described above with respect to thecontroller 40, the controller 228 operates to automatically move the rod252 and blade 248 out of engagement with the tubular structure 220 inresponse to movement of the trigger 212 in the second direction (thetrigger 212 being released by the operator).

It should be understood that, in some constructions, the controller 228may determine that the cutting mechanism has reached the secondcondition (when the tubular structure 220 is severed) or has reachedsome other selected condition (e.g., a condition between the firstcondition and the second condition) before the controller 228 willoperate to automatically return the cutting mechanism to the firstcondition if the trigger 212 is released. In such constructions, if theoperator releases the trigger 212 (the trigger 212 is moved in thesecond direction) before the tubular structure 220 is cut (or beforeanother condition has been reached), the controller 228 will notautomatically reverse the motor 224 to automatically move the blade 248out of engagement with the tubular structure 220. Rather, the cuttingmechanism will remain the in the same position until the trigger 212 isagain actuated.

FIGS. 9 and 10 illustrate a tube cutter 300 embodying one or moreindependent aspects of the invention. The tube cutter 300 includes ahousing 304. The housing 304 includes a handle 308 and a trigger 312.

The housing 304 supports a motor 316 (e.g., a DC motor) and a motorcontroller 320. The controller 320 is similar to or the same as themotor controller 40 described above. The controller 320 can include thesame or similar components as the motor controller 40 and can bemodified for application and use in the tube cutter 300. The controller320 operates in the same or similar manner as the motor controller 40.The motor 316 and the motor controller 320 can be powered by a varietyof sources such as a battery 324 (e.g., 12 volt, 14.4 volt, 18 volt,etc.). The battery 324 may be coupled to the handle 308.

The housing 304 supports a cutting mechanism 328. The cutting mechanism328 may be similar to that disclosed in U.S. Pat. Nos. 4,769,911;4,802,278; 5,495,672; 5,836,079; 6,065,212; and 6,202,307, the entirecontents of all of which are hereby incorporated by reference.

In the illustrated construction, the cutting mechanism 328 defines acloseable opening or recess 332. The cutting mechanism 328 supports adisc-like device 336 driven by the motor 316. The device 336 defines arecess 340 which is alignable with the recess 332. The recesses 332 and340 are configured to receive any size tubular structure 352 to be cut.It is noted that the tubular structure 352 is not limited to having acircular cross-section, but also includes structures with non-circularcross-sections.

The device 336 includes a plurality of rotatable blades 344 and aplurality of rolls 348. As the device 336 is rotated, the blades 344 areadvanced to cut the tubular structure 352 or retracted out of thetubular structure 352 (in response to the direction of rotation).

FIG. 11 is a flow chart illustrating the operation of the tube cutter300 to cut the tubular structure 352. In a first condition of thecutting mechanism 328, the recesses 332 and 340 are aligned to receive atubular structure 352. The operator positions (at 360) the cuttingmechanism 328 (e.g., the recesses 332 and 340) on the tubular structure352. The operator actuates (at 364) the trigger 312, which couples (at368) the battery 324 to the motor controller 320 and the motor 316. Withthe trigger 312 continuously actuated, the motor 316 rotates (at 372)the device 336. As the device 336 rotates, the recesses 332 and 340 movefrom being aligned to partially aligned, to misaligned, to partiallyaligned, to aligned, etc.

The blades 344 cut (at 376) the tubular structure 352 as the blades 344rotate with the device 336. When the tubular structure 352 is severed(the second condition of the cutting mechanism 328), the operatorreleases (at 380) the trigger 312, and the controller 320 causes themotor 316 to automatically reverse (at 384) until the recesses 332 and340 are in alignment (the first condition), such that the tube cutter300 can be removed from the tubular structure 352.

It should be understood that, when the trigger 312 is released, thecontroller 320 may cause operation of the motor 316 in the reversedirection to rotate the device 336 until the blades 344 are fullyretracted and until the recesses 332 and 340 are aligned so that thetubular structure 352 can be removed.

It should also be understood that, in some constructions, the controller320 may determine that the cutting mechanism 328 has reached the secondcondition (when the tubular structure 352 is severed) or has reachedsome other selected condition (e.g., a condition between the firstcondition and the second condition) before the controller 320 willoperate to automatically return the cutting mechanism 328 to the firstcondition if the trigger 312 is released. In such constructions, if theoperator releases the trigger 312 (the trigger 312 is moved in thesecond direction) before the tubular structure 352 is cut (or beforeanother condition has been reached), the controller 320 will notautomatically reverse the motor 316 to automatically align the recesses332 and 340 and/or to automatically move the blades 344 out ofengagement with the tubular structure 352. Rather, the cutting mechanism328 will remain the in the same position until the trigger 312 is againactuated.

FIG. 12 illustrates a tube cutter 400 embodying one or more independentaspects of the invention. The tube cutter 400 includes a housing 404.The housing 404 includes a handle 408 and a trigger 412.

The housing 404 supports a motor 416 (e.g., a DC motor) and a motorcontroller 420. The controller 420 is similar to or the same as themotor controller 40 described above. The controller 420 can include thesame or similar components as the motor controller 40 and can bemodified for application and use in the tube cutter 400. The controller420 operates in the same or similar manner as the motor controller 40.The motor 416 and the controller 420 can be powered by a variety ofsources such as a battery 424 (e.g., 12 volt, 14.4 volt, 18 volt, etc.).The battery 424 may be coupled to the handle 408.

The housing 404 supports a cutting mechanism. The cutting mechanism maybe similar to that disclosed in U.S. Pat. Nos. 3,839,791; 4,762,138;4,939,964; and 4,953,292, the entire contents of each of which arehereby incorporated by reference.

In the illustrated construction, the cutting mechanism generallyincludes a ring member 428 comprised of two generally semi-circularsections 432 and 436. The two sections 432 and 436 are connected by afastener 440, which allows the section 432 to pivot with respect to thesection 436 between an open position and a closed position.

In the illustrated construction, the ring member 428 supports adisc-like device 444 driven by the motor 416. The device 444 defines arecess 448. The ring member 428 and the recess 448 are configured toreceive any size tubular structure 460. It is noted that the tubularstructure 460 is not limited to having a circular cross-section, butalso includes structures with non-circular cross-sections. The device444 includes a rotatable blade 452 and a plurality of rolls 456.

FIG. 13 is a flow chart illustrating the operation of the tube cutter400 the tubular structure 460. In the first condition of the cuttingmechanism, the operator positions (at 480) the ring member 428 on thetubular structure 460, and the section 432 is closed and interconnectedwith the section 436.

The operator actuates (at 484) the trigger 412, which couples (at 488)the battery 424 to the motor controller 420 and the motor 416. With thetrigger 412 continuously actuated, the motor 416 rotates (at 496) thedevice 444. The blades 452 cut (at 500) the tubular structure 460 as theblades 452 rotate. When the tubular structure 460 is severed (the secondcondition of the cutting mechanism), the operator releases (at 504) thetrigger 412, and the controller 420 operates to cause the motor 416 toautomatically reverse (at 508) to align the ring member 428 and thedevice 444, such that the tube cutter 400 can be removed from thetubular structure 460.

It should also be understood that, in some constructions, the controller420 may determine that the cutting mechanism has reached the secondcondition (when the tubular structure 460 is severed) or has reachedsome other selected condition (e.g., a condition between the firstcondition and the second condition) before the controller 420 willoperate to automatically return the cutting mechanism to the firstcondition if the trigger 412 is released. In such constructions, if theoperator releases the trigger 412 (the trigger 412 is moved in thesecond direction) before the tubular structure 460 is cut (or beforeanother condition has been reached), the controller 420 will notautomatically reverse the motor 416 to automatically align the ringmember 428 and the device 444. Rather, the cutting mechanism will remainthe in the same position until the trigger 412 is again actuated.

In other constructions and in other aspects, the motor controller 40 canbe used in motor braking applications in power tools, such as, forexample, drills, reciprocating saws, circular saws, band saws, tablesaws, etc. U.S. Pat. No. 6,236,177 generally discloses a power toolincluding a braking and control circuit and is hereby incorporated byreference in its entirety.

There are two general categories of braking conditions, i.e., conditionsin which braking of the motor M is required or desired. The firstcategory includes safety-related braking conditions. In this category,braking of the motor M is required if an unsafe operating condition forthe power tool arises. For example, such a safety-related brakingcondition occurs when the tool element, such as a drill bit or a sawblade, binds on the workpiece causing the workpiece to jerk or kickback. In either of these safety-related braking conditions, braking ofthe motor M is required to prevent injury to the operator or damage tothe equipment or workpiece. Further, in such safety-related brakingconditions, braking of the motor M is accomplished as quickly aspossible without damaging the components of the motor M (e.g., the motorM is braked in 1 sec.).

The other category of braking conditions includes productivity-relatedbraking conditions. In this category, braking of the motor M is desiredto stop the associated tool element so that the operator can move to thenext drilling or cutting operation more quickly. The operator does nothave to wait for the tool element to coast to a stop before continuingoperations. Such productivity-related braking can be accomplished moreslowly than the safety-related braking to reduce the wear on the motor(e.g., the motor M is braked in 2 sec.). This is important becauseproductivity-related braking occurs more frequently than safety-relatedbraking. Generally, a productivity-related braking condition resultswhen the operator releases the trigger and on/off switch to disconnectthe motor from the power source.

The controller 40 and motor M can be modified for application and use inthe various power tools and electric-powered equipment for motor brakingoperations. The controller 40 operates in the same or similar manner asdescribed above for braking operations.

FIG. 14 is a flow chart illustrating the operation of a brakingapplication in a power tool or electric-powered device. The operatoractuates (at 520) the trigger 36, which couples (at 524) the battery Bto the motor controller 40 and the motor M. With the trigger 36continuously actuated, the motor M moves (at 528) a tool element. Whenthe operator releases (at 532) the trigger 36, the controller 40operates to cause the motor M to brake (at 536) by reversing direction.

It should be understood that, in some constructions, the controller 40may differentiate instances in which an operator has released somepressure on the trigger 36 (and allowed the trigger 36 to move in asecond direction) for reasons other than stopping operation of the powertool (e.g., to change the speed of the motor M (with a variable speedswitch), to adjust the grip on the power tool, etc.) from instances inwhich braking of the motor M is intended. In such constructions, thecontroller 40 may delay operation to reverse the motor M and to causebraking until the trigger 36 has moved a sufficient distance or for agiven time in the second direction (the release direction). If suchdelay conditions are not met, the controller 40 will allow the motor Mto continue driving operation of the tool element.

One or more independent features and independent advantages of theinvention may be set forth in the claims.

1. A power tool comprising: a housing; a motor supported by the housing,the motor operable in a first direction and a second direction; atrigger switch moveable in a first direction and a second direction; acontroller coupled to the motor and the trigger switch and beingoperable to sense actuation and deactuation of the trigger switch; afirst switch selectively coupled to the motor and the trigger switch,the first switch actuated when the trigger switch is moved in the firstdirection, and the motor being operable to move in the first direction;and a second switch selectively coupled to the motor and the triggerswitch, the second switch actuated when the trigger switch is moved apredetermined distance in the first direction for a predetermined periodof time, the first switch deactuated when the controller sensesdeactuation of the trigger switch, and the motor being operable to movein the second direction.
 2. A power tool as claimed in claim 1 whereinthe second switch is arranged in a parallel path to the trigger switch.3. A power tool as claimed in claim 1 wherein the trigger switchincludes a main switch and a potentiometer.
 4. A power tool as claimedin claim 3 wherein the second switch is actuated after the potentiometerreaches a threshold voltage for two seconds.
 5. A power tool as claimedin claim 4 wherein the threshold voltage is one volt.
 6. A power tool asclaimed in claim 1 wherein the power tool is a material dispensing gun.7. A power tool as claimed in claim 6 wherein the movement of thetrigger switch controls the speed at which material is dispensed.
 8. Apower tool as claimed in claim 1 wherein the second switch is deactuatedafter the trigger switch is released and 0.5 seconds after the motor isactuated in the second direction.
 9. A caulk gun comprising: a housing;a cradle supported by the housing and adapted to receive a caulk tube; abattery supported by the housing; a motor supported by the housing andselectively coupled to the battery, the motor operable in a firstdirection to dispense the caulk and in a second direction to reverseflow of the caulk; a trigger switch supported by the housing andoperable to actuate the motor in the first direction and the seconddirection; a secondary switch coupled in a parallel path to the triggerswitch, the secondary switch actuated a predetermined amount of timeafter the trigger switch is actuated, the motor operable in the seconddirection when the trigger switch is deactuated.
 10. A caulk gun asclaimed in claim 9 wherein the trigger switch includes a main switch anda potentiometer.
 11. A caulk gun as claimed in claim 10 wherein thesecondary switch is actuated after the potentiometer reaches a thresholdvoltage for two seconds.
 12. A caulk gun as claimed in claim 11 whereinthe threshold voltage is one volt.
 13. A caulk gun as claimed in claim 9wherein the movement of the trigger switch controls the speed at whichthe caulk is dispensed.
 14. A caulk gun as claimed in claim 9 whereinthe secondary switch is deactuated after the trigger switch is releasedand 0.5 seconds after the motor is actuated in the second direction. 15.A method of dispensing material, the method comprising the acts of:depressing a trigger switch; actuating a motor in a first direction tomove a plunger in a first direction, the plunger contacting the materialhousing to expel the material from the material housing; actuating asecondary switch after the trigger switch has been depressed apredetermined distance; releasing the trigger switch; and actuating themotor in a second direction to move the plunger in a second direction,the plunger moving out of contact with the material housing andreversing flow of the material.
 16. A method as claimed in claim 15 andfurther comprising deactuating the secondary switch after the motor isactuated in the second direction for a predetermined amount of time. 17.A method as claimed in claim 15 wherein the motor is moved in the firstdirection when the trigger switch has been depressed for a predeterminedamount of time.
 18. A method as claimed in claim 15 wherein the act ofdepressing the trigger switch further includes the act of controlling aspeed of the motor.
 19. A method as claimed in claim 15 furtherincluding the act of reading a voltage from the trigger switch.
 20. Amethod as claimed in claim 19 wherein the act of actuating the secondaryswitch occurs after the trigger switch reaches a threshold voltage fortwo seconds.